A highly efficient one-pot methodology is described for the synthesis of heparin and heparan sulfate oligosaccharides utilizing thioglycosides with well-defined reactivity as building blocks. L-ldopyranosyl and D-glucopyranosyl thioglycosides 5 and 10 were used as donors due to low reactivity of uronic acids as the glycosyl donors in the one-pot synthesis. The formation of uronic acids by a selective oxidation at C-6 was performed after assembly of the oligosaccharides. The efficiency of this programmable strategy with the flexibility for sulfate incorporation was demonstrated in the representative synthesis of disaccharides 17, 18, tetrasaccharide 23, and pentasaccharide 26.